First of all I have to say that my tumblr blog doesn’t have a custom domain. It was all working good before, the links from tumblr with preview as twitter cards, but it seems that now is on NSFW list (according to tumblr staff) so it’s not possible to display it as twitter cards anymore (instead, only shows links).
I’m asking a solution for this because I want to link my tumblr account to twitter, so I can show my posts like it was before with a simple preview from the posts I am publishing.

I can’t enter my tumblr domain to validate the implementation, it doesn’t accept the url.
I have my tumblr account linked to twitter in order to tweet everything I post.